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General Ecology (BIO 160) Dept. of Biological Sciences
Worksheet #4 Sacramento State University
Worksheet 4: Climate I & II
1. The Earth receives a wide range of solar radiation from the Sun. Which wavelengths of light
reaching the Earth’s surface make up visible light? __400-700 nm___ (pgs. 20-21)
2. Why does a 1 km2 area that is located between ±10o latitude receive more solar energy (i.e.,
greater solar heating) than a 1 km2 area located between 40-50o latitude? (pg. 21) Because
solar radiation hits the Earth’s surface more directly at ±10o latitude than at 40-50o latitude,
the amount of solar radiation per unit area (solar radiation density) at ±10o latitude is higher
than at 40-50o latitude. In other words, because the same amount of solar radiation is
spread out across a larger area at 40-50o latitude compared to ±10o latitude, the higher
latitude region has a lower solar radiation density than the ±10o latitude region.
3. Why is the summer solstice in the northern hemisphere in June and the summer solstice in
the southern hemisphere in December? How does the tilt of the Earth cause this
seasonality? (pgs. 21-22) The solstice occurs twice a year when the tilt of the Earth toward
or away from the sun is at its maximum. The maximum tilt of the northern hemisphere
toward the sun occurs in June (summer in the northern hemisphere) and away from the sun
in December (summer in the southern hemisphere). The tilt of the Earth causes the
seasonality because the solar radiation density on the Earth’s surface is most direct (and
thus highest) when the Earth is tilted toward the sun in the summer. It is the reverse in the
winter when the tilt of the Earth in the northern hemisphere is away from the sun.
4. As air rises it becomes cooler. What is this phenomenon called? Explain why this happens.
(pgs. 24-25, 27-28) Adiabatic cooling. Adiabatic cooling happens when an air mass
expands (and thus becomes less dense) with increasing altitude. As the rising air becomes
less dense, the internal energy of the substance decreases (that is, it traps less heat from its
surroundings). This phenomenon occurs at an average of 6 oC per 1,000 meters, but it can
vary.
Air (virtually) always contains sub microscopic droplets of water vapor, but as long as the
evaporation rate exceeds the condensation rate (which occurs at higher temperatures)
these drops do not persist. As rising air cools, the evaporation rate decreases more rapidly
than the condensation rate. As temperature drops, it reaches a point (the dew point
temperature) at which evaporation becomes less than the condensation and a droplet can
grow into a cloud drop.
5. Air masses circulate globally. What causes these air masses to circulate? (pgs. 25-26)
Differential solar heating at the equator causes air masses to rise and circulate in very large
atmospheric cells (e.g., Hadley cell) that move air masses around on a global scale.
6. Draw and label a diagram of a Hadley cell located at the equator. Explain how they occur
and what happens to the circulating air at each step. (pgs. 25-26; lecture)
Refer to the Climate lecture slide on Hadley cells.
General Ecology (BIO 160) Dept. of Biological Sciences
Worksheet #4 Sacramento State University
7. How does the Coriolis effect influence global wind patterns? In turn, how do these wind
patterns determine ocean circulation in the Pacific Ocean? (pgs. 25-26) As air moves from
high to low pressure, the Earth moves underneath it making the air curve to the right. In the
northern hemisphere, as air moves toward the equator it curves to the right and then runs
along the equator in an east to west direction. As the winds move across the ocean, they
drive ocean currents in the same direction. In the northern hemisphere, ocean currents
circulate in a clockwise direction, whereas in the southern hemisphere they circulate in a
counterclockwise direction.
8. Below is an illustration of a mountain range (~ 10,000 feet elevation), an ocean to its west,
and the prevailing wind direction. For each lettered location in the diagram (A - D), describe
the temperature and precipitation conditions (i.e., high, median, or low) you would expect to
occur at each location and why. (pgs. 24-25, 27-28, 30-31)
West East
C
B
Wind direction
A D
Ocean Mountain range
A. high temperature & low or median precipitation
B. median temperature & high precipitation
C. low temperature & median precipitation
D. highest temperature & lowest precipitation
9. What general weather conditions might you expect along the coast of California in an El
Niño year? Explain how an El Niño event would lead to these conditions. (pgs. 32-33)
Warm temperatures and high precipitation. This occurs because in El Niño years the trade
winds that normally blow warm moist air toward the western Pacific relax and cause this air
to accumulate in the eastern Pacific. California is affected by this climatic pattern and in an
El Niño year can experience warmer than usual temperatures and higher than usual
precipitation.
10. Explain how and why the rate of evaporation off the soil and the rate of transpiration (can
look up in Glossary of text) off plant surfaces (together termed evapotranspiration) differ
between south-facing and north-facing slopes in the northern hemisphere. (pg. 35, lecture)
Evapotranspiration is higher on south- than north-facing slopes because south-facing slopes
experience greater solar radiation densities than north-facing slopes. Because of the tilt of
the Earth, the sun’s rays hit south-facing slopes more directly and north-facing slopes more
obliquely. Solar radiation densities are lower (i.e., the energy of the sun is spread out
across a larger area) when the sun hits the Earth obliquely versus directly.
